Various polymeric coatings and articles are produced in processes involving use of organic solvents. Such processes require a latent catalyst or latent reaction promoter which can be activated in a controlled fashion. There is an intense effort by environmentalists, researches, law makers, and industry to promote high solids and 100% solids formulations and processes to reduce or eliminate use of such solvents and attendant costs and environmental contamination.
Various patents, e.g., U.S. Pat. Nos. 4,150,170 (Lazear); 4,181,752 (Martens); 4,330,590 (Vesley); 4,379,201 (Heilmann); and 4,391,687 (Vesley) disclose pressure-sensitive adhesives made via ultraviolet irradiation of a composition consisting of free-radically polymerizable monomers and a free-radical photoinitiator. These patents do not disclose use of more than one type of photopolymerizable monomer system, cationic organometallic photoinitiators, multiple photoinitiaton or use of polyurethanes in photopolymerizable pressure-sensitive adhesive compositions.
U.S. Pat. No. 4,415,615 (Esmay et al.) cellular pressure-sensitive adhesives comprising at least 15% voids.
WO 8802879 (Woods et al.) teaches a free-radically polymerizable composition comprising a free-radically polymerizable material and a photoinitiator system comprising a free-radical photoinitiator and a ferrocenium salt. The composition may contain one or more cationically polymerizable materials. No detail is provided as to the nature of these cationically polymerizable materials, nor do they teach use of multiphotoinitiation for energy irradiation. Polyurethane precursors are not disclosed. Pressure-sensitive adhesives with superior properties are not disclosed.
U.S. Pat. No. 4,849,320, (Irving) teaches an imaging system containing a combination of two different photoinitiators used with two different polymerizable monomers in combination with irradiation at two substantially different wavelengths. The monomers can be acrylate or epoxies or other cationically polymerizable monomers and the photoinitiators can include ferrocenium, onium salts or an alpha cleavage or homolytic bond cleavage photoinitiator. No polyurethane precursors thanes in such a photo initiation system is taught, nor pressure-sensitive adhesives.
E.P.O. 335629 (Rohm and Haas) discloses photoresists and printing plates comprising cationically polymerizable materials in combination with free-radically polymerizable materials, and photoinitiators for both materials. A photopolymerization process involving exposure to varied wavelengths of radiation is also disclosed. No polyurethanes are taught, nor any pressure-sensitive adhesives.
U.S. Pat. No. 3,661,618 (Brookman et al.) discloses a process wherein a solvent-free coating primarily comprising an acrylic ester monomer, is polymerized to a tacky state by being subjected to a beam of high energy electrons. Use of photoinitiators, multiple photoinitiation processes or polyurethanes is not disclosed.
E.P.O. 344,910, (Palazzotto et al.) discloses a photopolymerizable composition comprising a polymeric precursor, an optional photosensitizer and a two-component curing agent. Polymeric precursors are selected from ethylenically unsaturated monomers, epoxy and polyurethane monomers and specific mixtures thereof. The curing agent contains an organometallic salt and an onium salt. The compositions are generically disclosed to be useful as adhesives. No specific adhesive compositions or pressure-sensitive adhesives are disclosed.
E.P.O. 344,911 (DeVoe et al.) discloses a polymerizable composition comprising a polymeric precursor, a curing agent containing an organometallic salt and optionally a solvent. Polymeric precursors are selected from ethylenically-unsaturated monomers alone, and in combination with either polyurethane precursors or epoxy monomers. The compositions are generically disclosed to be useful as adhesives. No specific adhesive compositions or pressure-sensitive adhesives are disclosed.
U.S. Pat. No. 4,342,793, (Skinner et al.), discloses compositions containing unsaturated monomers and polyurethane precursors wherein the unsaturated monomers are radiation-curable. Radiation-curing of polyurethane precursors is not taught. No pressure-sensitive adhesives are disclosed.
It is an object of the invention to provide a pressure-sensitive adhesive using a set of polyurethane precursors in combination with at least one free-radically polymerizable monomer and a photoinitiator system containing at least one salt of a cationic organometallic complex.
It is a further object to provide an adhesive having good mechanical properties using preferred polyurethane precursors in combination with preferred free-radically polymerizable monomers.
It is a further object of the invention to provide a pressure-sensitive adhesive having good mechanical properties using an acrylate homopolymer, i.e., without the necessity of the addition of polar copolymerizable monomers.
It is a further object of the invention to provide pressure-sensitive adhesives containing both photopolymerized polyurethane components, and photopolymerized acrylic components having superior mechanical properties to comparative conventional acrylate adhesives.
It is a further object of the invention to provide multiple photoinitiation processes which provide control over polymerization order, thereby providing increased control over properties of the desired composition.
It is a further object of the invention to provide a multiple photoinitiation process for making a pressure-sensitive adhesive comprising at least one free-radically polymerized monomer, and one set of polyurethane precursors having superior mechanical adhesive properties to those of an identical adhesive otherwise polymerized.